1. Field of the Invention
This invention relates to an optical illumination assembly that provides a high degree of light transmission. More particularly, the invention is directed to an illumination assembly having a plurality of optical microprisms, microlenses and a diffuser for redirecting light from a light source.
2. Description of the Related Art
Optical illumination systems, such as backlit flat panel displays require a directed light source which provides an efficient output of light. Such displays are used in a wide variety of applications such as computer monitors, televisions, avionics displays, aerospace displays, automotive instrument panels, and other devices that provide text, graphs or video information. These displays can replace conventional cathode ray tubes and offer the advantages of lower profile, reduced weight and lower power consumption. There are many other illumination applications that can take advantage of such an illumination system employing such an arrangement of microprisms, microlenses and diffuser. Such applications exist in the automotive industry, the aerospace industry and the commercial and residential markets. Some automotive applications, include low profile car headlights and taillights; low profile interior car lights such as reading lights and map lights; light sources for dashboard displays; backlights for flat panel navigation displays, flat panel auto TV screens and flat panel electronic instrument displays; traffic lights; and backlights for road signs. Illustrative examples in the aerospace industry include backlights for flat panel cockpit displays and flat panel TV screens in the passenger section of the aircraft; low profile reading lights and aircraft landing lights; and runway landing lights. Residential and commercial applications include low profile interior and exterior spotlights and room lighting with a low degree of collimation; backlights for flat panel TV screens, LCD displays, such as computers, game displays, appliance displays, machine displays, picture phones, and rear projection displays including televisions and video walls.
One display which can eliminate the shortcomings of a cathode ray tube is the flat panel liquid crystal display (LCD). LCDs suffer from a number of inherent disadvantages. For example, at high viewing angles, LCDs exhibit low contrast and changes in visual chromaticity as the viewing angle changes. The characteristics of the backlighting apparatus are very important to both the quality of the image displayed by the matrix array of picture elements of the LCD and the profile of the display. See U.S. Pat. Nos. 5,128,783 and 5,161,041 for a discussion of the deficiencies in past backlighting configurations. Additionally, current backlighting systems, in applications such as laptop computers, are inefficient with regard to the amount of light that the viewer sees versus the light produced by the source. Only about ten to twenty percent of the light generated by the light source ends up being usefully transmitted through the computer display. Any increase in the light throughput will positively impact power consumption and ultimately increase the battery life of a portable computer and as a screen for rear projection displays. Accordingly, there exists a need in the flat panel electronic display art to provide a backlight assembly that provides an energy efficient and uniform light source for the electronic display while maintaining a narrow profile.
U.S. Pat. Nos. 5,555,109 and 5,396,350 provide an optical illumination system employing an array of microprisms attached to an array of microlenses via an intermediary spacer. Such a spacer adds an element of complexity to the described system. It also does not provide for the reception of diffuse light through a diffuser.
The present invention is directed to an improved illumination assembly which is useful for flat panel displays, having an improved backlight assembly which provides an energy efficient and uniform light source. The improvement by the use of the present invention is that an energy efficient, bright and uniform distribution of light is provided in a low profile assembly. The optical illumination assembly comprises an array of microprisms in combination an array of microlenses and an optional diffuser whereby the microprisms and optional diffuser are operatively disposed between light transmitting means and the microlenses.
The invention provides an illumination assembly comprising:
(a) a light transmitting means;
(b) an array of microprisms wherein each microprism comprises:
(i) a light input end optically coupled to said light transmitting means;
(ii) a light output end spaced from the light input end;
(iii) a pair of oppositely positioned first sidewalls, each first sidewall having an edge defined by said light input end and an edge defined by said light output end; at least one of said first sidewalls being positioned for effecting reflection of transmitted light toward the light output end;
(iv) a pair of oppositely positioned second sidewalls, each second sidewall having an edge defined by said light input end and an edge defined by said light output end; at least one of said second sidewalls being positioned for effecting reflection of transmitted light toward the light output end; and
(c) a microlens on the light output end of each microprism, such that when light from said light transmitting means enters each microprism through said light input end, the light is directed by said sidewalls through said microprisms and out each light output end.
The invention also provides an illumination assembly comprising:
(a) a light transmitting means;
(b) an array of microprisms wherein each microprism comprises:
(i) a light input end optically coupled to said light transmitting means;
(ii) a light output end spaced from the light input end;
(iii) a pair of oppositely positioned first sidewalls, each first sidewall having an edge defined by said light input end and an edge defined by said light output end; at least one of said first sidewalls being positioned for effecting reflection of transmitted light toward the light output end;
(iv) a pair of oppositely positioned second sidewalls, each second sidewall having an edge defined by said light input end and an edge defined by said light output end; at least one of said second sidewalls being positioned for effecting reflection of transmitted light toward the light output end; and
(c) a microlens on the light output end of each microprism, such that when light from said light transmitting means enters each microprism through said light input end, the light is directed by said sidewalls through said microprisms and out each light output end.
(d) a light diffusing element optically coupled between the light transmitting means and the light input end.